Each frame of video typically requires a large number of bits when recorded, converted and/or stored in a digital format. Further, video is often delivery at a rate of 30 frames per second. The large amount of digital data and the speed at which this data is delivered presents a large raw bandwidth requirement. Delivery of full content from broadcaster to customer is not practical. This drawback is overcome by compressing data through elimination of redundancies and other compression and encoding methods.
Many encoding models (e.g., MPEG) define and standardize decoding techniques, yet often do not restrict or define how encoders operate. Typically video is encoded to fixed bandwidth outputs with a constant bit rate (CBR), or encoded with a variable bit rate (VBR) where many bits are used for scenes with significant motion, and few bits for still scenes. For VBR there is still a target or maximum available bit rate specified for a given transport pipe. In operation, previous encoders are defined with either a CBR or VBR value, encoding begun, and the encoders are then left alone to produce an encoded output. The encoders continue to encode at the fixed encoding (CBR or VBR). Changes to an encoded bit rate typically includes stopping the encoder, redefining the parameters, reconfiguring the encoders to utilize the new parameters such that the encoders detect the new parameters and restarting the encoder with the new parameters.
In some applications, such as transmission over a wireless connection, the available bandwidth can change dynamically and suddenly. With CBR and VBR, the encoder continues to operate at the specified encoding bit rate regardless of the bandwidth capacity. If the bandwidth falls below a level that is required for the CBR or VBR content being pushed onto the communication link, data can be lost causing picture freezes and other discontinuities on a client display. Similarly, because encoders are started at a predefined bit rate and they continue to simply encode at that specified rate (CBR or VBR) without change, available bandwidth may be wasted when the encoded data does not occupy the entire bandwidth.